I have a complete model 28 LBXD with slide in base (LBXB) available. Prefer to not ship.

https://navy-radio.com/manuals/tty/sales/lbxd.pdf

It is 5 bit. I haven't checked which speed gears are installed, but I can do that if necessary
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The above comments or recommendations are SWAG. Use at your own risk.

John, W9DDD